Time averaging of signals consisting of rectangular pulses can be effected, e.g., by integration over at least one period of the rectangular signal or by low-pass filtering. Integration can be carried out by means of an up-down counter. A drawback for a processor, however, is then the necessary division by the value of the period, which may be relatively time-consuming.
In the case of low-pass filtering, the definite integral is replaced by an indefinite integral over the range -.infin..ltoreq.t.ltoreq.+.infin.. Accordingly, the transient response of the filter has to be taken into account, as otherwise the results are not exact.
Digital low-pass filters represent periodic networks with alternating pass and stop bands. As a pulse-shaped signal may have spectral components over a very wide frequency range, very accurate tuning of the low pass filter response and clock frequency with respect to the signal is necessary. The essential drawback of the low-pass filter consists in the high stop-band attenuation that has to be implemented. Because of these problems, excessively sophisticated circuitry will have to be implemented in order to achieve acceptable results.